1. Field of the Invention
The present invention relates to a flat-panel display device, and more particularly, to a flat-panel display device using an optical waveguide having high resolution of a reproduced image and high efficiency of light.
2. Description of the Related Art
Currently, cathode ray tubes (CRTs) are widely used as display devices for monitors or television sets. However, due to the drawbacks of the CRT being heavy and bulky, light flat-panel display devices such as liquid crystal display devices (LCDs) or plasma display devices are gradually being put into practical use. However, the LCDs are expensive and there are limits on the screen size. Plasma display devices are also expensive and consumes much power.
To overcome these disadvantages, display devices using optical waveguides have been developed. The optical waveguide is suitable for a display device having a large-sized screen because it can transmit bright light to a distant area with little attenuation of light.
FIG. 1 shows a conventional flat-panel display device using an optical waveguide.
The conventional flat-panel display device shown in FIG. 1 includes a core 15 into which the light output from a light source (not shown) is incident to then be propagated, a cladding 14 positioned on the core 15 and made of a material having a low refractive index so as to totally reflect the light propagated through the core 15, a light absorption layer 10 positioned on the cladding 14, for absorbing light, a first electrode 13 positioned on the light absorption layer 10 and to which a predetermined voltage is applied, an electro-optical material layer 16 positioned under the core and whose refractive index changes according to an electric field, a scattering layer 17 for scattering light, and a second electrode 18 which is grounded and made of a transparent material.
In the conventional flat-panel display device constructed as described above, if a predetermined voltage 12 is applied to the first electrode 13, an electric field 11 is generated between the first and second electrodes 13 and 18. The refractive index of the electro-optical material layer 16 increases due to the electric field 11 so that the light propagated through the core 15 passes through the electro-optical material layer 16 and collides with scattering particles in the scattering layer 17 to then be scattered. The light scattered in the scattering layer 17 passes through the second electrode 18 made of a transparent material so that light having passed through the second electrode 18 can be observed by a viewer.
However, in the aforementioned conventional flat-panel display device, since the scattering layer 17 has small particles causing scattering in all directions, the light incident into the scattering layer 17 is scattered in all directions and a considerable amount of light flux is reflected at the interface between the electro-optical material layer 16 and the scattering layer 17. Accordingly, only an extremely small amount of incident light is emitted to the outside. Thus, the light efficiency is very low.
Also, the conventional flat-panel display device cannot reduce the width of a waveguide for outputting light to less than a predetermined width because of its low output efficiency of light, which results in a limited resolution of a reproduced image.